New script to calculate average blocktime between block heights

To use the script:
    ./contrib/avg_blocktime.pl DRAGONX

It has some default block heights defined, if you want custom ones
than those are given as 2nd and 3rd arguments. Currently the script
prints out:

Avg blocktime over 3000 blocks = 36.0526666666667

So with this evidence it seems that DRAGONX has the correct average
blocktime and network hashrate.

contrib/avg_blocktime.pl

@@ -0,0 +1,57 @@
+#!/usr/bin/perl
+# Copyright (c) 2016-2022 The Hush developers
+# Distributed under the GPLv3 software license, see the accompanying
+# file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
+
+use warnings;
+use strict;
+my $cli     = "./src/hush-cli";
+my $coin    = shift || '';
+unless (-e $cli) {
+    die "$cli does not exist, aborting";
+}
+if ($coin) {
+    $cli .= " -ac_name=$coin";
+}
+my $getblock= "$cli getblock";
+my $start   = shift || 1850000;
+my $end     = shift || 1853000;
+
+my $blocks  = qx{$cli getblockcount};
+if($?) {
+    print "ERROR, is node running? exiting...\n";
+    exit 1;
+}
+
+if ($end > $blocks) {
+    print "The block $end is beyond how many blocks this node knows about, exiting...\n";
+    exit 1;
+}
+
+if ($start < 1) {
+    print "Invalid start block $start, exiting...\n";
+    exit 1;
+}
+
+my $block = $start;
+my $prev_blocktime = 0;
+my $total_duration = 0;
+
+while ($block <= $end) {
+	my $blocktime = qx{$getblock $block | grep time};
+    chomp $blocktime;
+    if($blocktime =~ m/(\d+)/) {
+        $blocktime = $1;
+    }
+    my $duration = $blocktime - $prev_blocktime;
+    if($prev_blocktime > 0) {
+        $total_duration += $duration;
+    }
+    #print "$block $blocktime $prev_blocktime $duration\n";
+    print "$block $duration\n";
+    $block++;
+    $prev_blocktime = $blocktime;
+}
+my $num_blocks = $end - $start;
+my $avg_duration = $total_duration / $num_blocks;
+print "Avg blocktime over $num_blocks blocks = $avg_duration\n";

contrib/block_time.pl

@@ -5,7 +5,7 @@
 use warnings;
 use strict;
 
-# Given a block time, estimate when it will happen
+# Given a block height, estimate when it will happen
 my $block      = shift || die "Usage: $0 123";
 my $coin       = shift || '';
 my $hush       = "./src/hush-cli";
@@ -30,7 +30,7 @@ if ($block <= $blockcount) {
     if ($coin eq 'DRAGONX') {
         $minpb = 0.6; # minutes per block
     } elsif ($coin) {
-        # TODO: support custom bloctimes
+        # TODO: support custom blocktimes
         $minpb = 1; # assumes default blocktime of 60s
     }
 	my $minutes = $diff*$minpb;